Diode Needed

Hello,
I have two car batteries, both running different loads.

The load on Battery A is often high amperage and the voltage is often highly variable, sometimes charging, sometimes discharging.
The load on Battery B is almost always of low amperage, but with a requirement that voltage remain relatively the same, around 12v or more.

When the voltage in Battery A is above the voltage of Battery B, I wish for it to charge Battery B.
When the voltage in Battery A is below the voltage of Battery B, I do not want it to discharge Battery B.

I would like to place two diodes between the two batteries on the two terminals which would allow current to go one way, thus Battery A to charge Battery B, but not to discharge it.

Would you kindly recommend the proper diode?

Thanks

How many amps can your charger supply?

The charger, connected only to Battery A can provide a maximum charge of 20 amps.

Then you need 40A (min) diodes. See if you can find some Schottky rectifiers. You will have to tweak the charger to compensate for the forward voltage drop across the diodes. Anodes to charger positive; cathodes to respective battery positive pole.

Would you kindly provide a type, perhaps a part # and supplier.

Thanks

DigiKey has **broken link removed**. Schottkys too, but they are expensive.